The electronic properties of a homoleptic bisphosphine Cu(I) complex: A joint theoretical and experimental insight

The origin of the optical properties of the firstly reported stable luminescent $\left[\text{Cu}\right(\text{PP}{)}_2{]}^{+}$ complex $\left[\text{Cu}\right(\text{dppb}{)}_2{]}^{+}[\text{dppb}=1\text{,}2-\text{bis}(\text{diphenylphosphino}\left)\text{benzene}\right]$ is investigated using the exchange–correlation functional PBE0. The choice of the basis set used is discussed and a comparison with the results obtained by other functionals is performed. The role played by the bisphosphine ligands within the complex is elucidated by considering the electronic properties of the ligand alone to evidence how both the geometrical changes and the electronic interactions, induced by the inclusion of the metal cation, affect the electronic behavior of the whole system. The NBO analysis shows how the aryl groups of the ligands act as a reservoir of electrons within the complex. The electronic excitations of both the complex and of the ligand, calculated by including the solvation effects, allow to assign the lowest energy absorption broad band, recorded in CH₂Cl₂ solution. The peculiar contribution of the phosphorus atoms to the description of the high occupied MOs and the participation of the copper cation to the description of the lowest singlet excited state, is pointed out. The origin of the observed phosphorescence of the complex is attributed to a triplet state, whose SOMO is characterized by the contributions of the valence 4s and of the Rydberg 5s AOs of the metal cation, along with the lone pair orbitals of the P atoms.